Radioreceiver



lMarch l5, 1932 T. c. vVAN TRABERT RADI'ORECEIVER original Filed Nov. 17. 1927 Q fjm ww@ @Eng a k *S will@ UN E? s RQ www" IN V EN TOR.

A TTORNE Y.

Patented Mar. 15, 1932 THEODORE C. VAN TRAIBERT, OF BRONX, NEW YORKl RADIORECEIVER Continuation of application Serial No. 233,748,11ed November '17, 1227. This application led January 23,

ieee. semi My invention relates to radio receivers and particularly to the circuit connections and apparatus of an improved receiverv that is particularly adapted for broadcast reception; this application being a continuation of my prior application, Ser. No. 233,748, filed November 17, 1927. Y

One object of the invention is to provide an improved receiver which employs ordinary amplifier tubes of the iilame'ntarycathode type but which does 'not require any batteries, acid rectifiers or the like.

Another object of my invention is to simplify the construction of the receiver without sacrificing volume or tone quality and to provide apparatus in Vwhich extraneousV noises and disturbances are reduced to a minimum.

Another object of my Vinvention is to provide an arrangement of circuits and apparatus in which amplifier tubes of the filamentary-cathode type m'ay be employed for amplifying signals or voice currents wherein the cathodes are energized directly from an alternatingcurrent source without introducing any alternating current hum such as is ordinarily obtained in an amplier of this character.

A still further object of my invention is to provide an improved B battery-eliminator of simple construction and which provides improved results in connection with the amplifier above referred to. i

The radio receiver embodying my invention may comprise filamentary-cathode tubes, such as those commonly designated las Type Q01-A, which are energized directly from an alternating current source, such as a stepdown transformer. These tubes are the cheapest and most highly developed and practical type of amplifier for the purpose available at the present time, and heretofore their use with alternating current cathode current has been considered undesirable because of the alternating current hum obtained in the output circuit. It is an important feature of my invention that by an improved circuit arrangement, not only is the alternating current hum completely elimm; mated without sacricing volume and tone quality, but it is found that the receiver is much less subject to extraneous disturbances caused by static conditions or the like which in the ordinary setrender thecharacter of the music or sound received displeasing or indistinct under all except idealv conditions. 1

Other vobjects and advantagesof Vmy invention will become apparent from consideration of the accompanying drawings, the single figure of which is a diagrammatic view of a radio receiving set embodying the invention.

Referring to the drawings,` the receiving set Vembodies an antennafcircuit l, a radio frequency amplifier 2, includingtlie amplifier tube 3, a detector 4 and an audiofrequency amplifier 5 including amplifier tubes 6 and 7.

The circuits of the set may be modified in various ways except inv respect to the portions described in detail hereinafter but for the purpose of disclosing the invention, a circuit including a tightly coupled tuned antenna circuit is shown togetherwith one stage of radio frequency amplification and a crystal detector. It will beV apparent from the following description ofthe invention that a loosely coupled antenna circuit may be employed or more than one stage of radio frequency amplification, either tuned or untuned, or an electro-ionic tube detector in place of the crystal detector 4.

The specific modification Vof the radio receiver which is shown in the drawing comprises two tuning controls which are variable condensers 8 and 9 in the antenna circuit and in the radio frequency amplifier, respectively. The only other controls that are necessary are a switch for turning o'ii7 the supply 'of power from the 110 volt alternating current circuit 10 to the set and avolume control, such as the variable resistance 11 bridged across the loud-speaker jack L. S. or connected in any well known manner to control the output current from the set. I

The antenna circuit includes the inductance coil 12 which forms with the condenser 3 a circuit which is resonant to the frequency being received, and fixed condensers 13 and A 14, respectively. The condensers 13 and 14 are connected in series relation in the antenna circuit and one terminal of the condenser 14 is connected to the usual ground connection.

The condenser 13 is of about 1/2 to 4 m. f. capacity, preferably 2 to 4 m. f., and is an essential Aelement of the circuit as will be explained hereinafter. The condenser 14 is of approximately 1/4 m. f. capacity and is only for the purpose of protection in case of an accidental short-circuit between the 110 volt supply circuit or other high-voltage circuit and the circuits of the radio receiver. This condenser may be omitted if desired without affecting the operation of the set.

. The antenna circuit is yconnected through airesistor 15 to the control electrode of the radio frequency amplifier tube 3. The resistance of the resistor 15 is appreciable'and may be relatively high for example a ballast resistance such as an .amperite and having a resistance of Vabout 25 ohms at l@ of an ampere may be used or a grid leak and parallel condenser may be used. The plate'electrode of the amplifier tube 3 is connected through a radio frequency transformer `16 tothe crystal detector 4, the secondary cir cuit of the transformer being tuned by the condenser 9 and containing a resistor 17 which may be another amperite7 of the same characteristics as that used in the input circuit of theamplifier tube 3.

, The crystal detector circuit is connected through audio-frequency transformers 20 and 21 and the audio-frequency amplifier tubes 6 and 7 in substantially the usual manner to the output circuit which is shown as connected to the loud-speaker jack L. S.

The dimensions and arrangement of the turning elements in the receiver depend upon the frequency of the current for which the set is designed to'respond and may be variously modified to meet the conditions encountered in actual practice. For a receiver designedto cover the present range of wavelengths frcm 200 to 600 meters, the condensers 8 and 9 may be of .0005 m. f. capacity, and the inductance l2 comprise about 2O to 50 turns of #24 enamelled wire kwound on a 31/8 inch bakelite tube, depending upon the length of the antenna and Whether a capacity antenna or loop antenna is used. The primary of the radio frequency transformer 16 may be of 32 turns of #24 enamelled wire on a 21/1- inch tube, preferably wound in two halves with 5/S inch spacing between the coil sections. The secondary winding may be 50 turns of the same wire on a 81/8 inch tube with the same spacing between the two halfsections. f-

The amplifier tubes 3, 6 and 7, and also the detector 4 where a vacuum tube detector is employed, are energized from the alternatingcurrent supply source 10 through aV step-down transformer 25 of the proper ratio to provide ABallast resistance having the proper characteristics may be substituted for 'these rheostats.

Two potentiometers 28 andY 29 areA also bridged across the cathodes of the radio and audio frequency amplifier tubes respectively. An inductance 0r similar impedance having a mid-point tap may be substituted for either of these potentiometers.

Although the control rheostats and the potentiometersare shown as variable, the voltawe of the standard lighting circuit is sufficientlv constant so that after these elements are initially adjusted to the proper point, no further adjustment is necessary. It is preferableto have the potentiometer 28 of rather high resistance, for example about 1800 ohms. The potentiometer 29 may be` of lower resistance. for example 300 ohms.

The supply of current for the plate circuits of the tubesis shown as a B-battery eliminator of the double-wave rectifier type, although ordinary batteries may be employed. This rectifier may be mounted in close proX- imity to or in the same cabinet with the receiver. Instead of using special rectifier tubes, I have found after considerable eX- perimentation that an exceedingly simple and practical rectifier may be constructed with the particular apparatus hereinafter described and using two Type 20L-A amplifier tubes as rectifiers. The rectifier tubes are indicated at 30 in the drawing. The filamentary cathodes of the tubes 30 are energized from a transformer 35 similar to the transformer 25, and the grid and plate electrodes of the tubes are'connected'together, as indicated'. v

The filter circuit of the rectifier includes two iron core chokes 31 in series with the output circuit of the rectifier, each choke having an inductance of approximately 30 henries. The bridging condensers 32 and 33 connected across the leads of the rectifier are preferably'of 4 m. f. and 8 m. f. capacity, respectively. In additiom'one of the choles 31 is shuntegd by a third condenser 34. of about 2 m. f. capacity.

The high potential for the rectifier may be obtained from any high grade step-up transforme-r which is connected to the supply circuit 10. However, I prefer to use two audio transformers 36 and 37 such as are commonly employed in the audio frequency amplifiers of radio sets and having a ratio of about 3 to 1. The transformers used for this purpose must be carefully chosen for good insulation and heat-dissipating capacity and should also have tightly clamped laminations so that no mechanical hum is introduced from this source. I have found that these transformers which are relatively inexpensivemay be connected for this purpose across a 110 volt supply circuit in the manner indicated without any appreciable temperature rise and with very satisfactory results. The transformers and chokes are preferably shielded from the set in the usual manner and the shield may be grounded to the usual ground connection. This ground connection may be either that shown in connection with the condenser 14 or the ground connection com- Amonly provided for .oneside of the supply circuit 10.

There are a number of factors which mustbe carefully considered in constructing a set of this `character to eliminate the alternating current hum with the use of alternatingcurrent filament supply without sacrificing volume and tone quality-and I have found that, besides the rheostats Vand potentiometers 26, 27, 28 and 29 already referred to, the resistors 15 and 17 and the condenser 13 are important factors. In addition, I have provided two other condensers, 4() and 41, each of approximately 2 m. f. capacity, the lirst being connected .to the tuned radio frequency vamplifier'circuit and the point 44 as indicated, and the second between the plus terminal of the plate current supply and the antenna circuit. The condenser 40 may be connected to the point 45 instead of the point 44, and the size of the condenser 41 may be as large as about 4 mff.

By a series of tests, I have proven that these elements connected as indicated and of the described characteristics are responsible for the improved results that are obtained. For example, if the condenser 13 be shortcircuited in a set that is built according to the diagram shown on the drawing, a pronounced alternating current hum is heard which cannot be eliminated by adjusting the filament controls 26, 27, 28 and 29.

From an inspection of the drawing it will be seen that condensers 13 and 41 are connected in series across the plate current supply source, 'and the grid circuits of all the amplifiers are connected to a point between the condensers. While I am unable to offer a satisfactory theory of operation, I have found by experiment that this particular arrangement of elements is effective in material.- ly reducing the interfering hum to a minimum. I have also found that an ordinary C battery of 4% volts may be substituted for condenser 18 Without any apparent change in operation, but in Iaccordance with one of the objects of my invention, I prefer to use an arrangement containing no batteries..

I am awarel that relatively lovsr resistances tatolr noises and static discharges and there is' also a decrease in the tendency of the set to produce an alternating current hum It seems `obvious that the result of the introduction of the resistances 15 and 17 is to substantially cut down the amplification ratio for currents appreciably different from the frequencies for which the circuitsvl and 2 are tuned, but I amunable to advance a theory of operation to explain this result.

The practical advantages o f a radio receiver embodying my invention lare many although perhaps'thefmost important is the production ofa simple and efficient setfusin'g tubes provided with filamentary cathodes but requiring no batteries or the like.` In rmany of the so-called electrical or batteryless sets being offered at the presenttime,there is an appreciable alternating current hum even though most of these sets embody tubes especially designed for this purpose and costing several times as much as the Type 201-A tube. It should be noted that all of the tubes in the present set are alike even those in the plate current rectifier, although the tube 7 may be a larger tube where the volume of output current is great. i

While the absence of alternating current hum in a set of this character is an important factor and one whichwill become more important as those using radio sets become more critical, the present set is also remarkable for its tone quality and vfreedom from extraneous noises. There appears to be no distortion in the voice currents received and the set is exceedingly quiet even when oper-v ated under conditions that are farfrom ideal.

Apparently the condensers 13, 40 and 41 serve to impro-ve the operation of the receiver in relation to its freedom from extraneous noises as well as in the elimination of alterhating current hum.

One of the sets has been operated in a locality where there are several motors connected to the circuit to which the setis connected and in a crowded area surrounded by apartment house buildings containing compressors and elevators. Even under these conditions the noise, which attains considerable volume in an ordinary receiver in this locality, is not only reduced so that it is not objectionable but it is substantially eliminated.

Furthermore, the receiver described is not appreciably affected by body7 capacity and ordinarily noshielding is provided'for the panel or the condensersv and. inductances.

Thedescribed arrangement and organizationof-the elements of a receiver may be modifiedy as .indicatedabove without departing from the spirit of the invention and I desire toinclude all such modifications and changes as fall within the scope of the appended claims. f

I claim: Y Y 1.A radio receiver .embodying an antenna circuit, a radio frequency amplifier, a detector and an audio frequency amplifier, said Aamplifiers 'comprising an electro-ionic vtube having a filamentary cathode, asource of alternating currentv for energizing ther cathodes lof said tubes, a potentiometer bridged across said cathodes, a condenser of relatively large capacity in series with the antenna circuit,

Vone terminal .of said condenser being connected to ground through a circuit having negligible yimpedance for radio-frequency currents anda connection between the lastmentioned terminal of said condenser and theintermediate tap on said potentiometer.

. 2. A radio receiver embodying an antenna cir-cuit, a radio frequency amplifier, aA detector and an yaudio frequencyampliiier, said amplifiers comprising tubes provided with cathode and grid and plate electrodes,.means for energizing said tubes and a condenser of the order of-2 m. f. capacity in the grid circuits of the amplifier tubes, oneterminal of said condenser being connected to ground .l through a circuit having negligible impedance for radio-frequency currents.

I 3. A radio receiver embodying an antenna circuit, a radio frequency amplifier, a det-ector and an audio frequency amplifier, said amplifiers comprising an electro-ionic tube having a filamentary cathode, a source of alternating current for energizing the cathodes of said tubes, and a condenser of approximately two m. f. capacity in series with the antennaV circuit, one terminal of said condenser being connected to ground through a circuit having negligible impedance for radiofrequency currents.

4. A radio receiver embodying an antenna circuit, a radio frequency amplifier, a detector and an audio frequency amplier, said amplifiers comprisingaii electro-ionic tube having a filamentary cathode, a source of alternating current for energizing the cathodes of said tubes, a condenser of relativelylarge capacity in the antenna circuit, one terminal of said condenser being connected to ground through a `circuit having negligible impedance for radio-frequency currents and a second f condenser connected between the last-nientioned terminal of the first-mentioned condenser and the plus terminal of the plate current supply source.

5. A radio receiver embodying an antenna circuit, a radio frequency amplifier, a detecof said tubes, a condenser of relatively large capacity in theantenna circuit, one terminal of said condenserfbeing connected to ground through a circuit having negligible impedance for radio-frequency current, and a condenser connected between the other terminal of the first-mentioned condenser and the plus terminal of the plate current supply source, the grid circuits of said amplifiers being connected to a point between said condensers.

6. An amplifier embodying a parallel-resonant circuit comprising inductance and capacity, an electro-ionic tube having itsinput electrode connected to oneof the terminals of said inductance and a relatively large condenser connected tothe other lterminal of said inductance and to ground through a circuit having negligible Vimpedance forradio-frequency currents..

7. A radio receiver embodying an antenna circuit, radio and audio frequency amplifiers of the filamentary cathode type provided with control electrodes and a detectonmeans for energizing the cathodes of said ampliers with alternating current, balancing circuits between the cathodes and ground -potential and a condenser of relatively large capacity connected in the antenna circuit, .said condenser being also in the cathode-controlelectrode circuit of the first radio frequency amplifier and traversed by the entire current flowing therein. Y

8. An amplifier comprising a thermionic relay having a filamentary cathode, a grid and a plate, a source of alternatingcurrent for energizing saidcathode, an input circuit connected at one side to the cathode circuit effectively at the electrical mid-point of said cathode and at the other side to said grid, said input circuit including a series condenser of relatively large capacity traversed by the entire( current flowing between cathode and gri 9. An amplifier comprising a thermionic relay having a filamentary cathode, a grid and a plate, input andoutput circuits for said relay, a source ofv energizing current in said output circuit having a disturbing component, a path across the terminals ofsaidsource including two condensers in series, one side of said input circuit Vbeing connected to said path between said condensers, and the other side being connected to the grid of the relay.v

l0. An amplifier comprising a thermionic relay having filament, grid and plate ele-k ments, a source of alternating currentvfor energizing said filament, a potentiometer in ter, a source of energizing current for the output circuit having a disturbing component, two condensers connected in seriesin a f path across said output current source, and an input circuit connected at one side to the grid element and at the other side to a, point between said condensers.

THEoDoRE o. VAN TRABERT. 

